Cutting Insert for Turning with Chip-Breaker Arrangement Providing Room for a Cooling Jet

ABSTRACT

A cutting insert includes a polygonal body of a hard, wear-resistant material, which has an upper surface and a lower surface, and a plurality of edge surfaces uniting said surfaces. At least one chip-breaker arrangement is provided in at least one of the lower and upper surfaces. At least one rounded cutting corner, provided with a nose-cutting edge, is formed at a nose portion at the area of the intersection area of two edge surfaces. The cutting corner defines a bisector. The chip-breaker arrangement includes two elongate chip-breaker segments having an opening provided therebetween intended to give room for a cooling jet directed toward the opening.

BACKGROUND AND SUMMARY

The present invention relates to a cutting insert for turning.

Many of the cutting inserts found today have some form of boss near thenose-cutting edge in order to form, lead, and/or angle the chip flow.Because of said design, it is difficult to come close to the cuttingzone and lift the chip by means of a high-pressure jet. This becomesespecially evident at flat angles of the high-pressure jet. In order tosolve this problem, use is made of entirely planar cutting plateswithout chip breakers, or cutting inserts without chip breakers near thenose-cutting edge and frequently in combination with very highpressures. Consequently, this brings about higher temperatures in thecutting insert and shorter service life, but also higher costs becauseof the expensive equipment and expensive operation. Furthermore, aplanar cutting insert entails high cutting forces. A known cuttinginsert has recesses, preferably near the cutting edge or even breakingthrough the cutting edge. The latter geometry cannot be used in practicein dry machining, since the edge will be weakened.

It is desirable to provide a cutting insert the chip breaker of which isespecially adapted to both dry machining and machining in combinationwith high-pressure cooling.

It is desirable to provide a cutting insert having improved service lifeand improved machining results.

It is desirable to provide a cutting insert that gives low cuttingforces.

It is desirable to provide a cutting insert that gives controlled chipforming.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A and 1B each shows a cutting corner in an embodiment of a cuttinginsert according to the present invention in plan view.

FIG. 1C shows the cutting corner in perspective view during chipbreaking with the assistance of a high-pressure jet.

FIG. 1D shows a schematic cross section through the cutting corner alongthe line S in FIG. 1C.

FIG. 2 shows a cutting corner in an alternative embodiment of a cuttinginsert according to the present invention in plan view.

FIG. 3 shows a cutting corner in an additional alternative embodiment ofa cutting insert according to the present invention in plan view.

FIG. 4A shows an additional alternative embodiment of a cutting insertaccording to the present invention in perspective view.

FIG. 4B shows a cutting corner of the cutting insert in FIG. 4A fromabove.

DETAILED DESCRIPTION

FIGS. 1A, 1B and 1C show a cutting corner 11 in an embodiment of acutting insert 10 according to the present invention. The cutting insert10 has a polygonal basic shape and may be double-sided. The cuttinginsert 10 is made from a hard, wear-resistant material, preferablycemented carbide, but may alternatively be of ceramics or cubic boronnitride (CBN). The most common hard material in cemented carbide iswolfram carbide, WC, and a binder metal. Alternative carbides may be ofthe metals titanium (TiC), tantalum (TaC) and niobium (NbC). The mostcommon binder metal is cobalt (Co), but also nickel (Ni) is found. Thecemented carbide is a powder mixture built up by carbide particleshaving grain sizes of 0.5-10 μm and a binder metal. The percentage byvolume of the binder metal is 5-40% and the percentage by volume of thecarbides is 95-60%. The cutting insert 10 is preferably coated with alayer of, e.g., Al2O3, TiN and/or TiCN.

The cutting insert 10 is developed to be used foremost in turning ofmetallic workpieces. The cutting insert has an upper surface 12 and alower surface, not shown, provided in separate, essentially parallelplanes, and a plurality of edge surfaces 13, 140 uniting said surfaces.The edge surfaces 13, 14 meet in rounded portions 21. The shown cuttinginsert 10 has a rhombic basic shape and comprises a central fasteninghole 15. The cutting insert may have two acute-angled cutting corners 11on each of the upper and lower surface. In the shown embodiment example,said tip angle is 80° but may alternatively be 55° or 60°. Cuttinginserts having perpendicular and other corners are also comprised in thepresent invention.

The upper side 12 has an essentially planar support surface 16, formedto abut against a base surface in a pocket of a holder, not shown. Thelimiting lines of the support surface 16 essentially follow the basicshape of the cutting insert. The support surface 16 may surround thefastening hole 15. In the embodiment illustrated, the two supportsurfaces 16 are essentially plane-parallel, the same extendingsubstantially perpendicularly to a centre axis of the hole 15.

Each cutting corner 11 comprises a portion 17 countersunk in relation tothe surface 16. In this case, the portion 17 is a sintered-inchip-former or chip breaker. The intersecting line between thecountersunk portion 17 and the edge surfaces 13 and 14 forms cuttingedges, i.e., a first cutting edge 18, a nose-cutting edge 19 and asecond cutting edge 20. The nose-cutting edge 19 is a substantiallypartly circular cutting edge, the radius of which is designated R andthe radius centre of which is designated Z. The cutting edges 18-20 maybe situated in a common plane.

At least one chip-breaker arrangement 22 may be provided in both thelower and upper surface 12, on one hand for lifting the chip during theturning and on the other hand so that both sides of the cutting insertshould be possible to be used in an economical way. In the preferredembodiment example, the upper and lower surfaces are identical butmirror-inverted so that when the cutting insert is indexed with thelower surface upward for turning, it has a geometry that is identical tothe upper surface 12. The cutting edges 18 and 20 of the cutting corner11 enclose an angle, the centre of which defines a bisector B. In thiscase, the chip-breaker arrangement 22 comprises two chip-breakersegments 22A, 22B, which have the purpose of lifting the chip andthereby allowing a high-pressure cooling jet 23 to come under the chipand closer to the cutting zone in order to, in this way, cool thecutting insert more efficiently and increase the service life of thecutting insert. The segments 22A, 22B are formed in such a way that anopening 24 is present between them, and thereby the possibility ofdirecting the high-pressure jet between them is given and hence lift thechip further. Here, by “opening”, reference is made to a generallycountersunk portion between two chip-breaker segments provided next toeach other. The segments 22A, 22B may connect somewhat to each other asis seen in the figures and are, in this case, arranged symmetrically inrelation to the bisector B.

With reference foremost to FIG. 1B, the designs and positions of thesegments 22A, 22B are described hereinafter. In this case, each segmentis elongate and has rounded ends. The size of the segment is determinedby the formula l×b×h, where, for instance, the length l=R×0.75 (R=thecorner radius), the width b=¼ and the height h=0.15-0.5 mm. The radiuscentre Z may be situated in the opening 24. The highest point of thesegment should not be arranged more than 0.25 mm above the associatedcutting edge 18, 20, but may also be arranged under the cutting edges orthe planes thereof The opening 24 between the segments 22A, 22B isdetermined by the formula: y=b/3, where y is measured symmetricallyaround the bisector and is at least 0.25 mm. The position of the segment22A, 22B in relation to the opposite cutting edge 18, 20 is chosen sothat the longitudinal axis S of the segment forms an angle α with theopposite cutting edge. The angle a that the segment forms with theopposite cutting edge 18, 20 may be within the interval of 10-50°,preferably within the interval of 20-40°, and most preferably about 32°.In the case the segments are arranged asymmetrically in relation to thebisector, the two segments 22A, 22B may be placed at different angles,see the description below in respect of FIGS. 4A and 4B. Each segment22A, 22B is placed X mm from the associated cutting edge, where X=R×Q.The factor Q of a conventional cutting insert is within the interval of0.3-0.5, while the factor Q of a wiper insert is within the interval of0.4-0.8.

The countersunk portion 17 comprises a chip surface 25 sloping downwardinward from the cutting edges 18-20. Frequently, a reinforcement bevel26 is provided in direct connection to the cutting edge 18-20. Eachsegment 22A, 22B protrudes from said chip surface 25. Thus, each segment22A, 22B has a similar inclination as the chip surface 25, obliquelyinward downward toward the bisector B, as is seen from the schematiccross section in FIG. 1D.

Furthermore, the countersunk portion 17 comprises a bottom surface 27provided essentially to form a space for the jet 23. Therefore, thecountersunk portion 17 is provided with a wall 28 running upward towardthe centre of the cutting insert. The wall 28 is displaced toward thecentre of the cutting insert from the segments 22A, 22B by a distancethat is at least equally large as the length 1 of the segment,preferably at least twice as large as the length l. The latter may alsobe described as the extension of the bottom surface 27 from the segmentstoward the centre of the cutting insert being at least equally large asthe length l of the segment, preferably at least twice as large as thelength l of the segment. The bottom surface 27 is essentially arrangedlower, i.e., arranged closer to the opposite lower surface, than thesegments and the wall.

In combination with or entirely independently of the chip-liftingsegments 22A, 22B mentioned above, moreover, the angle of the jet may befurther decreased in order to increase the accessibility by forming oneor more recesses 29 in the support surface of the cutting insert. InFIG. 1C, one recess is shown for the sake of clarity while in FIG. 1A,three recesses are shown. All recesses have successively increasingdepth and preferably also essentially increasing width toward the noseportion 21. The recess 29 may have a closed end 29A or an open end 29B,see FIG. 1A, turned from the nose portion 21. In a cross sectionperpendicular to the longitudinal axis of the recess, the recess may bedefined by one or more radii or comprise walls and bottoms. In the caseshown in FIG. 1A, three elongate recesses 29 have been arranged so thatthe longitudinal axis of each recess intersects the opening 24. Saidrecesses may be placed at different angles in relation to the bisector Bof the cutting corner in order to, in this way, give fixed positions forthe angle of the jet. These recesses 29 are arranged both in order toincrease the accessibility and to facilitate for the user to set thehigh-pressure jet at an angle making the jet to be directed against theopening 24 between the segments 22A, 22B. The chosen angle depends onthe cutting depth, feed, cutting speed as well as the material to beturned. It may be noted that the recess, in itself, is passive andthereby only constitutes a bore for a cooling jet, which emanates from anozzle provided separately from the cutting insert.

FIG. 2 shows a cutting corner in an alternative embodiment of a cuttinginsert according to the present invention, which differs from thecutting insert 10 shown in FIGS. 1A-1C in that five recesses have beenprovided in a fan shape with a common focus in order to increase thenumber of angles to set.

FIG. 3 shows a cutting corner in an alternative embodiment of a cuttinginsert according to the present invention, which differs from thecutting inserts shown in FIGS. 1A-1C and FIG. 2 in that a flute or aconcave groove 30 has been formed all the way out to the nose-cuttingedge 19 or to the reinforcement bevel 26. The concave groove 30 isarranged symmetrically around the bisector B in front of the segments22A, 22B and between the opening 24 and the rounded portion 21. Thereby,it is further ensured that the jet 23 comes as near the cutting zone aspossible. In doing so, the cooling jet 23 has the possibility of comingall the way up to the cutting zone as well as lifting the chipfurther—and decrease the wear of the cutting insert. With a cuttinginsert according to this invention, flatter angles can be used withoutbeing blocked by a chip breaker. Furthermore, the jet can come closer tothe cutting zone so that a lower pressure can be used in order toachieve a good chip-forming result. A lower pressure of the jet givesgreat advantages, foremost as for the service life the of the pumpequipment but also as for the dimensioning thereof. A pump equipment forhigh-pressure cooling is an expensive investment. Since the cost isproportional to the working pressure thereof, not only money is saved bymeans of longer worn-out time of the cutting insert but also thatequally high pressures do not need to be employed as in the use of atraditional chip breaker. Furthermore, from a safety and environmentalpoint of view, as low a pressure as possible in the system ispreferable. A lower pressure gives a safer handling and lower energyconsumption. Furthermore, the fixed positions, i.e., the recesses 29,for the angle of the jet to the bisector B on the top side of thecutting insert assist the user to set the cutting insert for optimummachining, as well as to increase the repetition accuracy of the cuttinginsert, since it is visually seen if the jet is positioned correctly.

The recesses on the top side of the cutting insert are generally notintended to cool the cutting insert, but rather to avoid blocking of thejet, i.e., to enable a further reduction of the inclination of the jet.

However, the cutting insert is not formed to be used together withhigh-pressure cooling only, but rather the opposite, i.e., it is acutting insert formed to operate with conventional cooling or with drymachining. By the fact that the cutting insert has a chip-breakerarrangement 22 divided in two parts near the nose-cutting edge, theportion works as an ordinary chip breaker in conventionally cooled aswell as dry machining. The two segments are arranged in such a way thatan opening 24 is present between them. Said opening 24 has twofunctions, on one hand the risk of crater wear is decreased, whichotherwise is common when the chip impinges on a conventional boss in thechip surface, and on the other hand a space is provided for thehigh-pressure jet to impinge under the chip. With high-pressure coolingapplications, here, pressures greater than 100 bar are intended.

FIGS. 4A and 4B show an alternative embodiment of a cutting insertaccording to the present invention that differs from the cutting insertsdescribed above in that the cutting insert is an example of anasymmetrical wiper insert, the shape of which is described closer in SEpatent No. 0201985-9, which hereby is incorporated in the descriptionwhat relates to the shapes of the cutting edges and of the clearancesurfaces. In this case, the segments 22A, 22B may be placedasymmetrically in relation to a bisector in the cutting corner by virtueof the feeding and cutting depth area of the cutting insert beingdifferently great dependent on how the cutting insert is used, i.e., ifit is longitudinal turning, facing or copying. In this case, thesegments 22A, 22B have a completely straight basic shape, as well as adistinct gap 24 between them. The segment 22A is associated with astraight cutting edge 18 under an acute angle, while the segment 22B isassociated with a curved cutting edge 19 under an angle of about 90°.

The recess 29 is provided in order to further decrease the angle ofinclination of the jet without being blocked by some part of the cuttinginsert, and also to guide the user to set the jet at the correct anglein relation to the cutting edge.

Thus, the present invention relates to a cutting insert for turning, thechip breaker of which, among other things, is especially adapted to bothdry machining and machining in combination with high-pressure cooling,having improved service life and improved machining results, which giveslow cutting forces and which gives controlled chip forming.

The disclosures in Swedish patent application Nos. 0501575-5 and0501576-3, from which this application claims priority are incorporatedherein by reference.

1. A cutting insert for turning, comprising a polygonal body of a hard,wear-resistant material, the body having an upper surface and a lowersurface, and a plurality of edge surfaces uniting the upper and lowersurfaces, at least one chip-breaker arrangement being provided in atleast one of the lower and upper surfaces, at least one rounded cuttingcorner, provided with a nose-cutting edge, being formed at a noseportion at the an area of intersection area of two edge surfaces, thecutting corner defining a bisector wherein the chip-breaker arrangementcomprises two elongate chip-breaker segments (22A,22B) having an openingprovided therebetween, the opening being adapted to give room for acooling jet directed toward the opening.
 2. Cutting insert according toclaim 1, wherein each segment has a length and a bottom surface isprovided between the segments and a center of the cutting insert, anextension of the bottom surface from the segments toward the center ofthe cutting insert being at least equally large as the length of thesegment.
 3. Cutting insert according to claim 1, wherein each segmentforms an acute angle with an opposite cutting edge.
 4. Cutting insertaccording to claim 1 wherein the segments are asymmetrically placed inrelation to the bisector.
 5. Cutting insert according to claim 1,wherein each segment has rounded ends.
 6. Cutting insert according toclaim 1, wherein the center of a corner radius of the cutting insert isarranged in the opening.
 7. Cutting insert according to claim 1, whereinthe opening between the segments is at least 0.25 mm.
 8. Cutting insertaccording to claim 1, wherein at least one recess is provided in asupport surface of the upper surface at a distance from the nose-cuttingedge, the recess having a general extension toward the nose portion, therecess being adapted to give room for a cooling jet directed toward thenose portion.
 9. Cutting insert according to claim 8, wherein eachrecess is elongate and has successively increasing depth toward the noseportion, the recess being adapted to give room for a cooling jetdirected toward the nose portion.
 10. Cutting insert according to claim8, wherein more than one recess is provided in the support surface and alongitudinal axis of each recess intersects the nose portion. 11.Cutting insert according to claim 2, wherein an extension of the bottomsurface from the segments toward the center of the cutting insert is attwice as large as the length of the segment.
 12. Cutting insertaccording to claim 5, wherein a size of each segment is determined by aformula l×b×h, where length l=R×0.75 (R=the corner radius) mm, width b=¼mm and height h=0.15-0.5 mm.
 13. Cutting insert according to claim 2,wherein each segment forms an acute angle with an opposite cutting edge.14. Cutting insert according to claim 2, wherein the segments areasymmetrically placed in relation to the bisector.
 15. Cutting insertaccording to claim 2, wherein each segment has rounded ends.
 16. Cuttinginsert according to claim 2, wherein the center of a corner radius ofthe cutting insert is arranged in the opening.
 17. Cutting insertaccording to claim 2, wherein the opening between the segments is atleast 0.25 mm.
 18. Cutting insert according to claim 2, wherein at leastone recess is provided in a support surface of the upper surface at adistance from the nose-cutting edge, the recess having a generalextension toward the nose portion, the recess being adapted to give roomfor a cooling jet directed toward the nose portion.
 19. Cutting insertaccording to claim 18, wherein each recess is elongate and hassuccessively increasing depth toward the nose portion, the recess beingadapted to give room for a cooling jet directed toward the nose portion.20. Cutting insert according to claim 18, wherein more than one recessis provided in the support surface and a longitudinal axis of eachrecess intersects the nose portion.